SEVERE OSTEOLYSIS OF THE PELVIS IN ASSOCIATION WITH ACETABULAR REPLACEMENT WITHOUT CEMENT

We reviewed the cases of fourteen patients (fifteen lesions) who had o steolysis following the replacement of the acetabulum without cement. Nine women and rive men, seventeen to sixty-seven years old, were invo lved in the study. One woman had bilateral pelvic osteolysis. Eight of the fifteen index acetabular reconstructions were done with a titaniu m-alloy implant and seven, with a chromium-cobalt-alloy implant. Eleve n of the fifteen acetabular components had holes in the metal shell th at may have acted as a conduit through which wear debris could gain ac cess to the implant-bone interface, but only two of the acetabular com ponents had been fixed with screws. In these two acetabular components , all available screw holes were not filled. The polyethylene liner wa s eight millimeters thick or less in twelve of the fifteen acetabular components; all of the liners were ten millimeters thick or less. The diameter of the head of eleven of the fifteen femoral components was t hirty-two millimeters. Fourteen of the fifteen femoral components were placed without cement, and all but one was radiographically stable. T he duration from the index operation to the appearance of pelvic osteo lysis ranged from fifty-three to eighty-four months (mean, sixty-five months). At the time of the diagnosis, the patients were functioning w ell clinically, and all but three had a Harris hip score of 90 points or better, despite extensive destruction of bone in some instances. Si nce these patients were functioning well, the pelvic osteolysis was di agnosed radiographically at a regular follow-up examination. Only one patient had evidence of migration of the acetabular component on seria l radiographs. Wear of the polyethylene liner was evident, on radiogra phic evaluation, in twelve of the fifteen hips. Nine patients (ten hip s) have been managed with a reoperation to date. In two of these hips, osteolysis was diagnosed before extensive destruction of bone had occ urred; in both hips, the lytic lesion was curetted and bone-grafting w as done in order to salvage the implant. In the other eight hips, the acetabular component was revised because of severe loss of bone, and a ll needed supplemental allografting. Histologically, the membranes wer e found to contain numerous macrophages. Particulate debris, consistin g predominantly of polyethylene, was present in all hips. Radiographs routinely led to an underestimation of the amount of bone loss; this f act emphasizes the importance of regular follow-up examination with se rial radiographs of good quality.